The present invention relates generally to an integrated process for the production of vinyl acetate and in particular to an integrated process for the production of vinyl acetate from a gaseous feedstock comprising essentially ethane.
Vinyl acetate is generally prepared commercially by contacting acetic acid and ethylene with molecular oxygen in the presence of a catalyst active for the production of vinyl acetate. Suitably, the catalyst may comprise palladium, an alkali metal acetate promoter and an optimal co-promoter (for example, gold or cadmium) on a catalyst support Acetic acid produced by carbonylation generally requires extensive purification to remove inter alia iodides arising from the catalyst system generally employed because iodides are recognised as potential vinyl acetate catalyst poisoners.
Combinations of processes for producing vinyl acetate are known in the art. Thus, WO 98/05620 discloses a process for the production of vinyl acetate and/or acetic acid which process comprises first contacting ethylene and/or ethane with oxygen to produce a first product stream comprising acetic acid, water and ethylene, contacting in a second reaction, one in the presence or absence of additional ethylene and/or acetic acid the first product stream with oxygen to produce a second product stream comprising vinyl acetate, water, acetic acid and optionally ethylene; separating the product stream from the second step by distillation into an overhead azeotrope fraction comprising vinyl acetate and water and a base fraction comprising acetic acid; either recovering acetic acid from the base fraction and optionally recyling the azeotrope fraction or recovering vinyl acetate from the azeotrope fraction. The catalysts suggested in WO 98/05620 for the oxidation of ethylene to acetic acid or ethane to acidic acid are catalysts of the formula
PdaMbTiPcOx
with M being selected from Cd, Au, Zn, Ti, alkali metals and alkaline earth metals; other catalysts for the oxidation of ethane to acetic acid are catalysts of the formula
VPaMbOx
with M being selected from Co, Cu, Re, Fe, Ni, Nb, Cr, W, U. Ta, Ti, Zr, Zn, Hf, Mn, Pt, Pd. Sn, Sb, Bi, Ce, As, Ag and Au or
catalysts for the oxidation of ethane and/or ethylene to form ethylene and/or acetic acid which catalysts comprise the elements A, X and Y, wherein
A is ModReeWf and wherein X is Cr, Mn, Nb, Ta, V or W and wherein Y is Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Ti or U.
Other catalysts for the oxidation of ethane to acetic acid and ethylene suggested in WO 98/05620 are those of the formula
MoxVyZz
with Z being selected from Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Sc, Y, La, Ce, Al, Tl, Ti, Zr, Hf, Pb, Nb, Ta, As, Sb, Bi, Cr, W, U, Te, Fe, Co, Ni. U.S. Pat. No. 5,185,308 which is cited in WO 98/05620 describes examples wherein space time yields in the range between 555 and 993 g vinyl acetate per hour per liter catalyst are achieved.